You should be able to do this with calculation fields. The calculations can pad/truncate the data so that each column of data has exactly the same number of characters.
To be clear, with your solution, if I was exporting 42 fields, I woudl have to create 42 duplicate fields that used teh calculation to pad each file to eth required length?
And if the extra length is filled with spaces, wodul FileMaker export respect that and not truncate trailing spaces?
(This is a requirement of a mainframe system that needs to see each field of specific lengths, filled with spaces, in order to import data)
Yes, you'd need 42 calculation fields. If the result type selected for these fields, trailing spaces would not be trunated, though I would have guessed that you'd need to add leading spaces rather than trailing.